It is essential from the standpoint of the efficient use of elevator systems in buildings to know the passenger flows inside the building and how many passengers are in the elevator cars in different operating situations. More particularly information about passengers arriving in the elevator cars and exiting from them on each landing gives detailed information about the passenger flows of the buildings, from which it is possible to compile, among other things, statistics for evaluating and for improving the efficiency of the use of the elevator systems. By means of statistics it is also possible to estimate the service need of elevator systems and to prepare forecasts of the numbers of passengers to be served. Up-to-date information about the numbers of passengers in elevator cars can, for its part, be utilized in different operating situations, such as e.g. in interruptions to the operation of the elevator. As a result of the advantages to be achieved, the need for measuring passenger flows often becomes a issue to address when modernizing old elevator systems and/or when installing a condition monitoring system in an elevator system, in connection with which it is desired to integrate the monitoring of passenger traffic.
The movement of elevator passengers into the elevator car and out of the elevator car is in prior art determined by using door photoelectric cells for detecting the movement of people or by measuring the load of the elevator car by means of a so-called car load weighing device e.g. during a stop of the elevator. The separating capability of a photoelectric cell is however limited in peak-traffic situations, especially if there is simultaneous traffic in both directions at the doors. When using load information, the load of the elevator at the time of stopping, at the time of starting, and the smallest load during the time between these, has been measured. From these results the number of incoming and outgoing passengers has been calculated utilizing the average weight of a passenger. In the method it is assumed that all the exiting passengers leave the car before the incoming passengers step into the car, which does not correspond to the real situation. The divergences of the weight of actual people and the weight of a normalized elevator passenger also cause an inaccuracy.
One prior-art solution is disclosed in patent application EP0528188, in which the arrival in the car and departure of passengers is detected from changes occurring in the signal of the car load weighing device. The method improves the method presented above that is based on the signal of the load weighing device but is however imprecise owing to the inaccuracy of the signal of the load weighing device and the limited frequency response of the car load weighing device. More particularly the solution is difficult to implement when modernizing elevators because connecting to the load-weighing signal can be awkward or the elevator car totally lacks a car load weighing device.
An acceleration sensor can be used in an elevator system for many kinds of measurements. For example, the acceleration of the elevator car can be monitored with an acceleration sensor. From the measurements given by from the sensor it is possible to calculate, in addition to acceleration, e.g. the position of the elevator in the elevator shaft and the stopping accuracy of the elevator floor by floor. Overall a very comprehensive view of the operation of the whole elevator can be formed from the measurement results of the acceleration sensor. One possible embodiment of an acceleration sensor in connection with elevator systems is to detect the arrival/departure of passengers into the elevator car/out of the elevator car by means of an acceleration sensor fixed to the elevator car.
Acceleration measurement in itself is not usually adequate as a basis for signal processing, but instead generally it is necessary to integrate in order to ascertain more accurate results. In this case so-called bias problems (deviations) caused by installation errors of the sensor are inevitably encountered. Bias problems are caused by, among other things, the acceleration sensor never being in practice fully perpendicular with respect to the direction of movement to be measured. In addition, if the acceleration sensor is installed on the roof of the elevator, it inclines dynamically with the car as the loading of the car changes. FIG. 1 illustrates one such situation.
In FIG. 1 the elevator is standing at a floor with passengers exiting and arriving in the car. The upper curve in FIG. 1 presents a situation in which the acceleration as such is integrated into speed v(t) and speed, for its part, into position x(t).
                                          v            ⁡                          (              t              )                                =                                                    v                0                            +                                                ∫                                      T                    0                                    T                                ⁢                                                      a                    ⁡                                          (                      t                      )                                                        ⁢                                                                          ⁢                                      ⅆ                    t                                                                        ≈                                          ∑                                  k                  =                  1                                N                            ⁢                                                a                  ⁡                                      (                    k                    )                                                  ⁢                Δ                ⁢                                                                  ⁢                t                                                    ⁢                                  ⁢                              x            ⁡                          (              t              )                                =                                                    x                0                            +                                                ∫                                      T                    0                                    T                                ⁢                                                      v                    ⁡                                          (                      t                      )                                                        ⁢                                                                          ⁢                                      ⅆ                    t                                                                        ≈                                          ∑                                  k                  =                  1                                N                            ⁢                                                v                  ⁡                                      (                    k                    )                                                  ⁢                Δ                ⁢                                                                  ⁢                t                                                                        (        1        )            where v0=0, x0=0, T0=the moment when the door is open and passengers are able to move and T is the moment in time when the closing stage of the door starts, Δt is the discrete interval (sampling interval) and N is the number of samples.
As is seen from FIG. 1, the error caused by the inclination of the car accumulates in the integration, in which case speed and position “escape” uncontrollably. It is possible to attempt to improve the situation with the fact that the speed of the car at the start and at the end of the loading cycle is zero:
                                                        v              ⋒                        ⁡                          (              t              )                                =                                                    ∫                                  T                  0                                T                            ⁢                                                a                  ⁡                                      (                    t                    )                                                  ⁢                                                                  ⁢                                  ⅆ                  t                                                      ≈                                          ∑                                  k                  =                  1                                N                            ⁢                                                a                  ⁡                                      (                    k                    )                                                  ⁢                Δ                ⁢                                                                  ⁢                t                                                    ⁢                                  ⁢                                            a              _                        b                    =                                                                      v                  ⋒                                ⁡                                  (                  T                  )                                            -              0                                      T              -                              T                0                                                    ⁢                                  ⁢                              v            ⁡                          (              t              )                                =                                                    ∫                                  T                  0                                T                            ⁢                                                (                                                            a                      ⁡                                              (                        t                        )                                                              ⁢                                                                                  -                                                                  a                        _                                            b                                                        )                                ⁢                                  ⅆ                  t                                                      ≈                                          ∑                                  k                  =                  1                                N                            ⁢                                                (                                                            a                      ⁡                                              (                        k                        )                                                              -                                                                  a                        _                                            b                                                        )                                ⁢                Δ                ⁢                                                                  ⁢                t                                                    ⁢                                  ⁢                              x            ⁡                          (              t              )                                =                                                    ∫                                  T                  0                                T                            ⁢                                                v                  ⁡                                      (                    t                    )                                                  ⁢                                                                  ⁢                                  ⅆ                  t                                                      ≈                                          ∑                                  k                  =                  1                                N                            ⁢                                                v                  ⁡                                      (                    k                    )                                                  ⁢                Δ                ⁢                                                                  ⁢                t                                                                        (        2        )            
The above integrates at first the measured acceleration for calculating the speed {circumflex over (v)}(t), the average error āb for acceleration is calculated from the final error of speed (the end condition of integration is that the speed of the car must be zero). With this term the speed v(t) and finally the position x(t) are integrated again from the corrected acceleration. From the lower curve of FIG. 1 it is seen that the situation improves slightly, but not however sufficiently. The deviations in the position of the car produced by the passengers are generally of the order of magnitude of hundreds of micrometers and at their maximum of some millimeters. In the lower curve of FIG. 1 the calculated deviation of the car is approx. 50 mm. On the basis of FIG. 1 it is seen that the deviations in the position of the car produced by the passengers are lost in the errors caused by inclination of the car and reliable detection of the passengers from a signal thus corrected is very problematic.